1. Field of the Invention
The present invention relates to a method of installation of an ion exchange membrane to an electrolytic cell. More particularly, it relates to a method of installation of a cation exchange membrane of a fluorinated polymer having carboxylic acid groups as the ion exchange groups to an electrolytic cell, preferably a finger type electrolic cell has been equipped with abestos diaphragms.
2. Description of the Prior Arts
In a process for producing an alkali metal hydroxide by an electrolysis of an alkali metal chloride, a membrane process has been mainly employed instead of the mercury process in view of prevention of a public pollution. As a membrane process, a process using a diaphragm such as a asbestos diaphragm has been industrially employed.
It has been known, as an electrolytic cell using asbestos diaphragm, to use Diamond Shamrock cell and Hooker cell which are finger type electrolytic cells wherein many anodes are fixed to stand from a bottom of the cell and many finger type cathodes coated with each asbestos diaphragm are inserted between the anodes to cover them. However, the alkali metal hydroxide obtained by the asbestos diaphragm process has a low concentration and contains the impurity of the alkali metal chloride whereby the alkali metal hydroxide can not be directly used for many industrial uses such as productions of industrial chemicals.
Various processes using an ion exchange membrane instead of the asbestos diaphragm have been proposed to obtain an alkali metal hydroxide having high purity and high concentration. In view of an alkaline resistance and a chemical resistance, a cation exchange membrane of a fluorinated polymer is preferably used as such membrane. In view of a production of an alkali metal hydroxide with high concentration at high current efficiency, carboxylic acid groups are preferably selected as the cation exchange groups.
When a conventional electrolyic cell equipped with asbestos diaphragms remains in a factory, if said ion exchange membrane is equipped in the conventional electrolytic cell instead of the asbestos diaphragm, the cost for installation is only small and an alkali metal hydroxide having high purity and high concentration can be obtained. When a cation exchange membrane of a fluorinated polymer having carboxylic acid groups as ion exchange groups is used for an electrolysis of an alkali metal chloride, the membrane is in a form of an alkali metal form as the alkali metal of the alkali metal hydroxide such as sodium form as the terminals of the carboxylic acid groups.
Thus, according to various studies, when a cation exchange membrane of a fluorinated polymer having carboxylic acid groups in the alkali metal form is used to install to a cell to cover each electrode such as in a bag form, the membrane has less flexibility not to easily perform the work and the membrane is easily damaged or teared by corners or edges of the electrode in the forcible installation of the membrane. Such trouble has been found in the use of the cation exchange membrane having carboxylic acid groups having the formula EQU --(COO).sub.m X
wherein X represents an alkali metal atom or alkaline earth metal atom or --NHRR'R" and R, R' and R" respectively represent hydrogen atom or a lower alkyl group and m is a valence of X. On the other hand, according to various studies, it has been found that a membrane has a desired flexibility to easily install the membrane to cover the electrode especially to cover the electrode in a bag form without any damage and without any substantial deterioration of electrolytic characteristics in the use of the cation exchange membrane having carboxylic acid groups having the formula EQU --COOL
wherein L represents hydrogen atom or a C.sub.1 -C.sub.20 alkyl group.
In finger type electrolytic cells such as Diamond Shamrock cell and Hooker cell, anodes and cathodes are arranged to insert each electrode between the other polar electrodes in an assembly of the electolytic cell. In this case, when the membrane having carboxylic acid groups in the form of --(COO).sub.m X is covered on the electrodes having the same polarity in the assembly of the electolytic cell, the covered membrane is damaged or teared by collision or friction with the counter electrodes.